The United Nations said Tuesday that its chemical weapons inspection team has delayed a second trip to the site of an alleged chemical weapons attack in Syria to shore up security, the Associated Press reports.

The announcement followed a statement from the Syrian Foreign Minister that U.N. team was delayed because of disputes between rebel groups.

Unidentified attackers fired on the U.N. convoy on its initial trip Monday morning, and the team was forced to turn back temporarily to replace a damaged vehicle. The team plans to delay its second trip by a day and return on Wednesday. The Obama administration said Monday that it’s “undeniable” Syrian forces used chemical weapons in the outside Damascus that killed hundreds last week, and western governments are increasingly mulling a military intervention.